You can avoid the embarrassment of a delayed meal because the turkey is not fully done. Oven temperature, cooking method and the size and initial temperature of the turkey breast all influence how long it takes to get a fully cooked roast.
Track the Temperature
Oven temperatures can vary as much as -3.89 degrees C depending on altitude, the size and type of oven, humidity and whether you are cooking indoors or outside. How close or far the roasting pan is from the cooking element will also affect how long it takes to cook. The thermostat controlling the oven may not be calibrated accurately. Whatever you cook, from turkey to tapas, will be influenced by the variations in temperature. Use an oven thermometer to get an accurate reading of your oven's temperature.
The temperature of the turkey breast at the beginning of the roasting process also affects cooking time. A frozen or partially thawed piece of meat will take longer to cook. Place the turkey roast in the oven only when it is completely thawed. Have a meat thermometer handy to ensure that the meat reaches a temperature that kills any possible bacteria. For turkey, the safe temperature is 73.9 degrees C.
Chose the Method
Your turkey will cook more quickly if you cook it with an enclosed method rather than open. You can enclose the turkey in a lidded turkey roasting pan, in a baking bag or in a clay baking dish with a lid. It will take longer if you keep the turkey under an aluminium foil tent. Roasting pans and clay baking dishes absorb heat and keep it close to the roast. Aluminium foil keeps heat from overcooking the breast skin. Dark baking pans heat food more quickly than shiny ones, and smaller pans push the roast to done faster than larger pans. Some people advocate roasting the turkey at a single temperature, while others cook the turkey at a lower temperature to start with and then raise the temperature 51.7 degrees C for the final half-hour. When using a barbecue, smoker or rotisserie, remember that the outside temperature, wind chill and humidity will all affect cooking time. Cooking time will be longer the larger the size of the roast, and the thicker the breast.
Putting it all together
The best way to gauge cooking time for a formal dinner is to do a trial run or runs. You will become familiar with what your oven does with the size roast you plan to serve and you can try the results out on yourself rather than your guests. You can experiment with various preparations--marinades, brining, basting, placing spices under the skin or wrapping it in salt pork to see which most closely approaches the time and taste you want.